This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Applications No. 198 55 996.8, filed on Dec. 4, 1998, and No. 198 49 430.0, filed on Oct. 27, 1998, the entire disclosures of which are incorporated herein by reference through the parent case U.S. Ser. No. 09/433,191 the priority of which is also claimed under 35 USC 120.
The invention relates to monitoring a part driven by an electric motor. The part may, for example, be a motor driven vehicle window or a tool. In many instances it is desirable to provide information whether a part driven by an electric motor is moving, if so in which direction the part is moving, and which position has been reached. In the case of a vehicle window, especially a rear window, the respective information is used for controlling an electrically driven window lifter to provide an anti-jamming function. The invention also relates to a circuit arrangement for carrying out such monitoring.
A group of known devices for detecting the position and the direction of rotation of a power driven part makes use of 2-channel sensor systems which provide signals that are phase-shifted and evaluated in an electronic unit. The sensors used can operate in accordance with different physical principles, e.g. electrical, magnetic, inductive, and optical.
For example, the electric motor drive disclosed in EP 0,359,853 Al makes use of two Hall sensors displaced at an angle to each other and allocated to a ring magnet attached to an armature shaft. When the armature shaft rotates, the two Hall sensors generate two correspondingly phase-shifted signals that are digitized and then evaluated in an electronic unit. After processing, the respective signals represent the only basis for identifying the direction of rotation. Since the corresponding signal pattern is characteristically different for each direction of rotation, the counted pulses can be allocated unequivocally to a definite direction of rotation.
However, the known technical solution mentioned above requires no fewer than two sensor channels, whereby it needs a correspondingly high number of components and conductors for its implementation. Also, the construction space to be provided for the installation can have a negative effect, especially when using small drive units with integrated electronics.
When only one such sensor is used, only one signal exists which is proportional to the number of the revolutions made by the motor and which is then allocated to one direction of motion of the driven part in accordance with the polarity of the motor drive voltage. The signal must be added to or subtracted from the previous position, whichever applies. Signal flanks that occur after the motor drive voltage has been switched off cannot be assigned.
Japanese Patent Publication JP 63-304307 A discloses a velocity control for a motor drive wherein the phase difference between a velocity control pulse and an incremental pulse of a length measuring laser device is continuously acquired. The control circuit used in said Japanese disclosure further includes a pulse converter and a mechanism for transforming the rotary motion of the motor into a linear motion. An up or a down count signal is generated in a transformer from the measurement of the linear motion in accordance with the direction of the positioning command.
The teaching described above does permit a very accurate control of the adjustment velocity of a driven part but it is not suitable. for establishing at the same time its position. Further measures must be provided for this purpose.
Furthermore, German Patent Publication DE 43 15 637 C2 discloses a method for detecting the position and direction of rotation of a drive. Not only the signal flanks of the digitized sensor signal but also the status of the drive is taken into account in that in the event of a direction reversal of the rotation the signal flanks are allocated in accordance with an overshoot time that is limited by fixed time thresholds. On principle, these time thresholds can be determined empirically or calculated mathematically. Adaptation to widely varying system conditions is not possible because the variation of the motor current over a period of time when the direction of rotation reverses, varies by several orders of magnitude. In particular, a control with fixed thresholds is always limited solely to a specific load situation, which is essentially determined by the external moment to be overcome. A current rise due, for instance, to a window pane freezing or jamming does lead to deviations. In motor vehicles, the operating supply voltage can drop quite considerably if the battery is about dead and other electrical power using elements are also being operated. If the electric motor is used very frequently, as is the case, for example, in actuating drives on industrial machine tools, the electrical parameters of the motor also change because of the warming effect. If the time thresholds were to be placed so far apart that all these cases could still be detected, then a particularly smooth running actuator arrangement would perform several revolutions in the opposite direction before being detected by the threshold. 0,603,506 A2 describes a method for determining with a position encoder the position of a part driven in two directions by an electric motor in motor vehicles, wherein a change in the movement direction is to be identified according to the duration of a break period between two pulses from the position encoder.
Errors can occur in such a method due to a rapid change of direction or if the motion of the part is non-uniform and does not take place in a single step.
The applicant""s DE 197 33 581 C1, which is not a prior publication, describes a method for measuring the motor current at the latest at the time of driving switching devices for the purpose of switching over the motor voltage from one direction of motion to the opposite direction. On changing the polarity of the externally supplied motor drive voltage, the motor current displays a characteristic curve due to the overshoot as a result of the mass inertia of the motor and the part moved by it, for instance the window pane and its mechanical drive transmission. A voltage that opposes this reversal of direction of motion is induced and superimposed on the external motor drive voltage and causes the characteristic curve of the motor current from which the actual moment in time for the reversal of direction of motion is derived as a function of time, which is considerably later than the time at which the motor drive voltage changes over. The signal flanks of the sensor signal are added to or subtracted from the actual position by the signal evaluation according to the actual direction of motion. This electromechanical behavior of d.c. motors is described by means of so-called motor equations.
In a series of tests it has been found, however, that because of other effects, deviations continue to occur in the position determination. These deviations are not negligible and cumulate over the life of a vehicle.
A substantial cause for the above mentioned deviations that continue to occur in the position determination are signal flanks that arise even after switching off the motor drive voltage. Particularly, after stopping the motor, an overshoot or run-out of the motor occurs because of inertia, which has been neglected heretofore. Such motor run-out can, however, continue for a duration corresponding to several motor revolutions causing respective signal flanks which are not evaluated or which are incorrectly evaluated. Further, this fault is not always compensated by a corresponding run-out in the opposite direction of motion.
The disclosure of Japanese Patent Publication JP 07-222477 A, published on Aug. 18, 1995 has recognized that each of these changes in the motor rotation direction results in a voltage induction in accordance with the generator principle. These deviations, however, occur when the motor is already switched off from the motor drive voltage. Therefore, it is possible to ascertain the generator voltage and to make possible an allocation of the generator voltage signal flanks to the actual motion direction.
For a number of uses it is, however, necessary to stop the motor as quickly as possible. Such stopping takes place conventionally by short-circuiting the winding terminals of the motor. A respective circuit arrangement for a braking action is, for example disclosed in U.S. Pat. No. 4,319,170. However, the rotation direction of the motor is not taken into account in the known braking action circuit.
As is disclosed in said JP 07-222477 A, the generator voltage cannot be measured or ascertained during the existence of the short-circuit. Therefore, it is suggested in Japanese publication JP 07-222477A to open again briefly the switches that short-circuit the motor to cause a brief no-load run and to measure and evaluate the generator voltage that occurs during this no-load run. Such a temporary ascertaining of the generator voltage, however, requires a noticeably increased effort and expense for the motor control and delays the braking action of the motor. Moreover, the method according to the above Japanese publication is still subject to deviations due to erroneous allocation of signal flanks.
In view of the foregoing it is the aim of the invention to further improve and to simultaneously simplify a method for recognizing the motion, the motion direction and the position of a component that is driven by an electric motor, which for example, opens or closes a car window. It is also an object to provide a circuit arrangement for the performance of said method. Another important object of the invention is to determine the rotation direction of an electric motor that has been short-circuited for applying a quick braking action to the electric motor without the need for any temporary interruption of the short-circuit of the motor.
A motion direction of a component drivable by an electric motor is detected according to the following steps. First, the electric motor is switched on for rotation in a desired direction of rotation by applying a respectively polarized motor drive voltage to the windings of the electric motor. Second, the polarized motor drive voltage of the electric motor is switched off and the electric motor is simultaneously short-circuited while the motor keeps running by reason of inertia whereby the motor temporarily operates as a generator which generates or induces a generator or inertia current. Third, the induced generator current or inertia current of said electric motor following the switch-off is measured or sensed to provide a motion signal that contains motion and motion direction information regarding the motion of the drivable component. The motion direction is based on the polarity of the induced generator current. Fourth, the motion signal is evaluated to obtain said motion and direction information for further use, such as controlling the motor. Short-circuiting the motor while measuring or sensing the inertia current has the advantage that the time duration of continued rotation following switch-off is reduced and the circuit arrangement is simplified.
According to the invention there is further provided a circuit arrangement for measuring an induced generator current that is produced by inertia rotation of an electric motor following stopping said electric motor by short-circuiting. The present circuit arrangement includes the electric motor, a drive voltage source (UB) and a reference potential connectable or connected to the motor through switching devices for operatively connecting windings of said electric motor to said operating voltage source and to said reference potential for normally driving said electric motor to rotate in a desired rotation direction. At least one voltage drop producing electric circuit element such as a measuring resistor or a diode or even a diode inherent in the switching devices is operatively connected to the electric motor. The switching devices are further connectable for short-circuiting the electric motor through the at least one voltage drop producing electric circuit element for inducing a voltage drop that is proportional to the induced generator current. At least one electric measuring circuit is connected to the voltage drop producing electric circuit element for measuring the voltage drop and for producing a measured signal representing the induced generator current.
By short-circuiting the drive motor for applying a breaking action and measuring an induced generator current also referred to as inertia current that is generated by the motor run-out caused by inertia, the invention achieves the important advantage that the generator current can be continuously measured during the run-out without interrupting the active braking action applied to the motor. More specifically, interrupting the short-circuiting of the motor is avoided. Further, by measuring the generator current during run-out following the short-circuiting a more precise control is assured because a number of deviations are now taken into account which heretofore went unrecognized. As a result, sensed signal flanks are correctly allocated to the respective movement direction. Thus, the method of the invention is capable of taking into account deviations that can be caused by external forces outside the drive system for the operation of the motor driven component such as a car window. For example, mechanical vibrations which move the component, or a spring-back action when the component encounters a stop, can cause such deviations. Any structural elements such as rubber dampers inside the motor, tension springs forming enclosures of a cable pull connecting the motor to the movable component or rubber buffers or seals have a certain elasticity that can cause the spring-back action, since these elements are first tensioned by the run-out of the motor whereby energy is stored and then dissipated by causing the spring-back action. Any deviations caused by the above mentioned structural elements are taken into account by the invention.
Further embodiments of the present method take all run-out and spring-back characteristics of the component drive system into account as well as the motion direction of the driven component prior to switch-off and any motion in the opposite direction due to said spring-back. Moreover, other movements of the motor can be detected. Such other motor movements are, for example, caused by mechanical forces, while the motor drive voltage is switched off. The features of the further embodiments are capable to take such motor movements into account. Once the motion direction is ascertained and known the signal flanks of the sensor output signals can be added to or subtracted from the previous component position thereby providing motion direction information.
The circuit arrangement according to the invention comprises in the short-circuit branch an electrical circuit element for producing a voltage drop between the motor winding terminals which are short circuited for stopping the motor. For example, separate measuring shunt resistors can be used for this purpose. In another embodiment the internal resistance of a circuit element, particularly the motor switching device, is capable of producing a sufficiently large voltage drop that can be used for the present purposes.
The measuring resistor may be divided into several measuring resistors. Instead of providing the measuring resistor or shunt resistor as one or more separate circuit components, it is possible to provide the measuring resistor in the form of a printed circuit resistor. In another embodiment the voltage drop is measured across a diode which is connected to the circuit to be conducting in the generator current flow direction so as to pass the generator current that is produced as a result of short-circuiting the motor. The conductive state voltage drop across the diode is approximately 0.7 volts which corresponds to the given threshold generator voltage. Compared to measuring a voltage drop across a resistor, the diode has the advantage of a considerably lower internal resistance. In both instances the voltage drop is a measure for the respective generator current.
The present circuit arrangements permit not only measuring of the generator current. Rather, the present circuits can also be used for measuring the motor drive current when the motor drive voltage is applied, in particular also for detecting the time at which a reversal of a motion direction takes place when changing the direction of the motor drive voltage.